package org.apache.lucene.analysis;

/**
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import java.io.IOException;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.List;

import org.apache.lucene.util.AttributeSource;

/**
 * This class can be used if the token attributes of a TokenStream
 * are intended to be consumed more than once. It caches
 * all token attribute states locally in a List.
 * 
 * <P>CachingTokenFilter implements the optional method
 * {@link TokenStream#reset()}, which repositions the
 * stream to the first Token. 
 */
public final class CachingTokenFilter extends TokenFilter {
    private List<AttributeSource.State> cache = null;
    private Iterator<AttributeSource.State> iterator = null;
    private AttributeSource.State finalState;

    public CachingTokenFilter(TokenStream input) {
        super(input);
    }

    @Override
    public final boolean incrementToken() throws IOException {
        if (cache == null) {
            // fill cache lazily
            cache = new LinkedList<AttributeSource.State>();
            fillCache();
            iterator = cache.iterator();
        }

        if (!iterator.hasNext()) {
            // the cache is exhausted, return false
            return false;
        }
        // Since the TokenFilter can be reset, the tokens need to be preserved as immutable.
        restoreState(iterator.next());
        return true;
    }

    @Override
    public final void end() throws IOException {
        if (finalState != null) {
            restoreState(finalState);
        }
    }

    @Override
    public void reset() throws IOException {
        if (cache != null) {
            iterator = cache.iterator();
        }
    }

    private void fillCache() throws IOException {
        while (input.incrementToken()) {
            cache.add(captureState());
        }
        // capture final state
        input.end();
        finalState = captureState();
    }

}
